The present invention relates to a label printing device, particularly although not exclusively as may be used in a weighing scale.
Commodity items such as fresh foods, e.g. fresh meat, fish, fruit and vegetables, are often sold by weight. Fresh food departments, such as deli departments in supermarkets which utilise slicers or the like to dispense food products from a bulk quantity, use weighing scales to weigh the dispensed product. Based on its price per unit weight the scale calculates a sub-total price of the item or dispensed product. A printing device incorporated into the weighing scale then prints a label showing the sub-total price and/or a barcode which is scanned at a Point-of-Sale (POS) or check-out register. The blank labels for printing on are removably adhered in series at prescribed intervals on a roll of backing paper and held in a cassette or cartridge that can be inserted into and extracted from the weighing scale to enable the operator to change the roll whenever it runs out. Typically, a label cassette in the art includes a feed reel or hub for holding a roll of labels on a backing paper, a drive roller or capstan assembly to drive the labels over a peeling edge, and a take-up reel or hub for taking up the expended backing paper once the labels have been removed from it. The drive roller assembly typically comprises a rubber drive roller and a metal pinch roller between which the labels and their backing paper are fed. The backing paper is somewhat more flexible than the label itself. After printing, each label is separated from the backing paper simply by bending the backing paper sharply away from the label, which is usually done by drawing the backing paper over a fairly sharp edge or peeling edge. The less flexible label then separates from the backing paper. It is important that there is sufficient tension in the backing paper so as to enable the label to separate as the backing paper is fed over the peeling edge. In order to maintain the tension of the backing paper between the drive roller and the take-up reel, both the drive roller and the take-up reel in prior art label cassettes are driven by one motor or by respective motors in the weighing scale and are mechanically linked in the cassette by means of a gearing assembly or by means of a drive belt which drivingly engages the motor(s) in the scale when the cassette is in place. For example a gear in the cassette gear assembly may engage with a motor driven gear in the weighing scale.
However, as the backing paper is continually wound onto the take-up hub, the take-up reel radius increases and hence the take-up hub has to turn more slowly, given a substantially fixed label feeding speed governed by the drive roller assembly. The variable rotational speed of the take-up hub relative to the drive roller is compensated for by means of a slip clutch on the take-up hub/reel. The slip clutch acts so that the torque on the take-up hub/reel is kept below a predetermined threshold. If the torque exceeds this threshold the clutch slips thereby preventing the backing paper between the drive roller and the take-up hub/reel from ripping. However, by maintaining a constant torque, a change in the radius of the backing paper wound onto the take-up hub will cause the tension of the backing paper between the take-up hub and the drive roller to change. In an extreme case, (when the take-up hub is empty or near empty) the tension may go beyond a predetermined threshold of the backing paper causing the paper to rip. At the other extreme, with a full or near-full take-up hub, the backing paper may become slack, thereby creating a loop of backing paper between the take-up hub/reel and the drive roller which may become entangled within the cassette. Such slackness may also result in the bend in the backing paper around the peeling edge becoming insufficiently sharp to separate the printed labels, which are therefore rolled up on the take-up reel/hub, rather than being dispensed.
Replacing an expended label roll with a fresh label roll typically requires manually feeding a free end of the label roll through guides within the label cassette from feed reel/hub through the drive roller assembly and onto the take-up reel/hub. This is very time consuming and inconvenient to customers if carried out whilst they are waiting at a service counter or till. This problem is addressed by keeping at least one “spare” cassette which is loaded with fresh labels “offline” whenever convenient, whilst the other cassette is “online”, i.e. in use in the weighing scale. When the “online” cassette is exhausted, it can be simply exchanged for the full “offline” cassette, thereby minimising scale downtime. The now empty “offline” cassette can then be refilled before the “online” cassette runs out again. However, the number of label cassette devices that a supermarket or convenience store can hold is very much dependent upon their cost. They tend to be expensive due to the many different mechanical components which they contain. A typical label cassette as taught in JP2009014455 (Ishida Seisakusho) comprises a drive roller assembly, a take-up hub and a gear assembly to mechanically link both of these for driving engagement with drive means in the scale. All of these components are supported on a metallic chassis and housed in a plastic covering.
Despite time saving measures at the service counter or check-out by keeping spare loaded label cassettes, there is still an increasing emphasis in supermarkets to further reduce waiting times and simplify the procedure for changing label cassettes. The number of operations to change a typical label cassette in a weighing scale is usually three or more. These include any one of the following procedures:                i) releasing a door to access the area of the label cassette,        ii) lifting the printing head to disengage it from the label or backing paper of the expended cassette,        iii) removing the expended cassette        iv) inserting a new cassette        v) re-engaging the print-head on the fresh label/backing paper        vi) closing the access door.        
In an attempt to reduce the number of operations required to replace an expended label cassette device, JP2009014455 (Ishida Seisakusho), describes a front loading label cassette for a weighing scale in which the print head rocks open and closed in a vertical direction with the insertion or extraction of the label cassette. This reduces the number of operations to replace the label cassette in a weighing scale to only one operation. However, despite the improvements made in reducing the number of operations, this has not reduced the complexity and manufacturing expense of the label cassette. Hence there is reluctance by shop owners and managers to keep sufficient numbers of spare label cassettes. Thus there is a need to provide a low cost label cassette device that can be inserted into and extracted from a weighing scale with a minimum number of operations.
Whereas an operator recognises that a till roll is nearly finished by means of a mark such as a red line on the last remaining portion the roll, no such indication method exists for labels. Even if such marks are used, not only does this destroy the aesthetic appearance of the last few remaining labels but in some cases would take the operator by surprise and therefore, offers the operator very little opportunity and time to make preparations to change the supply roll for a fresh roll of labels. One way the industry has tried to tackle this problem is by providing quick changeable label cassettes as described above. More sophisticated methods involve using software techniques whereby a sensor and a processor count the number of labels dispensed from the print head mechanism and knowing the number of labels on a fully charged roll, the remaining number of labels on the roll can thus be calculated. When the remaining number of labels reduces to a predetermined threshold quantity, the weighing scale provides a warning to the operator that the labels are about to run out. Although feasible, this method still suffers from a number of drawbacks. Firstly, the technique will only work when the roll is changed whilst the weighing scale is left powered on or in an active state and if changed when the scale is de-activated, the memory needs to be reset to erase counts from a previous roll. If, for example, an operator de-activates the weighing scale and changes the roll well before a roll end warning has been given, the processor will still have a record of the number of labels dispensed from the previous roll. When the weighing scale is re-activated, this number together with the number of labels dispensed from the new roll leads to confusion as the threshold number of labels dispensed is reached early and the processor provides warning signals to the operator well before the new roll has actually run out. Thus, there is a need to provide a cassette device to be removably mounted in or to a printing device of a weighing scale, that indicates when the roll of labels is coming to its end, and which does not suffer from the above problems.
It is necessary in label printing machines that the label on its backing paper is accurately positioned adjacent the print head. This becomes more critical where a label such as found in typical a supermarket is divided into areas separated by borders, each area being printed with specific information associated with the commodity item such as a barcode, the price per unit weight, the subtotal, other product specific information, or general information, special offers, etc. To enable the printing device to locate designated areas of the label, it is necessary that the portion of the label for printing is positioned in registration with a print line of the print head, otherwise a portion of the label ahead of the print head line becomes wasted. Prior art labelling machines as taught in U.S. Pat. No. 5,556,492 (Vonderhorst, J. P) utilise a label sensor positioned along the feed path through the labelling machine to sense the label, the gaps between the labels or other indicia on the backing paper or labels and to send signals to a controller for controlling stopping and starting of the drive roller at the precise time required. To make full use of the area of the label, prior art label cassette devices try to re-position a blank label on the backing paper so that the selected area is aligned with the print line of the print head after the previously printed label is issued. Such re-positioning methods involve rotating the drive roller assembly and the take-up hub backwards a sufficient amount so that the next blank label is positioned in registration with the print line of the print head. This rewinding is necessary because, in order to fully peel off and present a printed label to a customer/sales assistant for detachment from the backing paper, the next label on the backing paper is transported beyond the ideal first line printing position. The problem associated with this method is that to ensure that the previous printed label has been detached, the rewinding does not take place until the weighing scale has been activated for printing the next label. There is thus a dead time following printing activation until the printing device re-positions the next blank label properly in registration with the print line of the print head before printing starts. The customer therefore experiences the noise of the motors driving the labels and carrier paper backwards but there is a delay before a printed label actually emerges. In an extreme case, this can leave the customer or operator frustrated particularly as this delay can be significant when attempting to print a number of labels. Thus a continuous printing mechanism for labels is required that does not suffer from the above problems of the delay and “noise without apparent useful activity”.